Most of the bronchodilators used at present for the therapy of diseases showing tracheal abnormality such as asthma are .beta.-adrenoceptor stimulants as typically represented by isoproterenol, terbutaline, salbutamol, trimetoquinol and the like and their pharmacological action is based on that they stimulate .beta.-adrenoceptors in tracheal smooth muscles to dilate the muscles. It is, however, well known clinically that these pharmaceutical agents also act on .beta.-adrenoceptors present in other sites than tracheal smooth muscles and cause serious side effects such as tachycardia, vasodilatation, tremor and the like. These known bronchodilators, therefore, have a serious defect that they have to be used, upon administration, with a sufficient care for the above side effect and depending on the patient's pathological conditions. It is therefore considered at present that the essential condition for desired bronchodilators are that they selectively act only to the tracheal smooth muscles.
The inventors of the present application have made various studies for developing new pharmaceutical agents free from the foregoing defects and, as the result, discovered that the compounds represented by the above general formula (I) are very useful as new type bronchodilators in view of their mechanism of action and chemical structure, different from conventional .beta.-adrenoceptor stimulants, in that they selectively act on the tracheal smooth muscles to thereby provide relaxation therein while causing only very weak cardiovascular effects. The present invention has been accomplished based on the above findings.
It is known that the compounds represented by the following general formula: ##STR2## where R' represents n-propyl, n-butyl, cyclohexyl, phenyl, benzyl and phenetyl, R" represents lower dialkylamino, X represents oxygen or sulfur atom and A represents an organic or inorganic acid has a local anesthetic action as disclosed in Japanese Pat. No. 426,718 (Japanese Patent Publication No. 1671/1964), Folia Pharmacol Japan [vol. 58, p 67-77 (1962)] and the like.
The local anesthetic action of the compound having the following general formula: ##STR3## where R', R" and A have the same meaning as above, is also disclosed in Japanese Pat. No. 426,717.
Further, Japanese Pat. No. 277,099 (Japanese Patent Publication No. 18278/1960) also describes that the compound represented by the following general formula: ##STR4## where R is alkyl, R.sub.1 and R.sub.2 individually represent methyl or form a heterocyclic ring together with nitrogen atom, has an antibiotic effect against influenza virus.
None of these known literatures, however, contain descriptions which suggest the bronchodilatation action of the compounds according to the present invention.